Section 2 Electron Configuration and the Periodic Table

Objectives Explain the relationship between electrons in sublevels and the length of each period of the periodic table. Locate and name the four blocks of the periodic table. Explain the reasons for these names.

Objectives, continued Discuss the relationship between group configurations and group numbers. Describe the locations in the periodic table and the general properties of the alkali metals, the alkaline-earth metals, the halogens, and the noble gases.

Periods and Blocks of the Periodic Table Elements are arranged vertically in the periodic table in groups that share similar chemical properties. Elements are also organized horizontally in rows, or periods. The length of each period is determined by the number of electrons that can occupy the sublevels being filled in that period. ¢ The periodic table is divided into four blocks, the s, p, d, and f blocks. The name of each block is determined by the electron sublevel being filled in that block.

S,P,D, & F Blocks

Group 1 Metals The elements of Group 1 of the periodic table are known as the alkali metals. lithium, sodium, potassium, rubidium, cesium, and francium In their pure state, all of the alkali metals have a silvery appearance and are soft enough to cut with a knife.

Sodium

Group 2 Metals The elements of Group 2 of the periodic table are called the alkaline-earth metals. beryllium, magnesium, calcium, strontium, barium, and radium Group 2 metals are less reactive than the alkali metals, but are still too reactive to be found in nature in pure form.

Calcium

Hydrogen & Helium Hydrogen has an electron configuration of 1s1, but despite the ns1 configuration, it does not share the same properties as the elements of Group 1. Hydrogen is a unique element. Like the Group 2 elements, helium has an ns2 group configuration. Yet it is part of Group 18. Because its highest occupied energy level is filled by two electrons, helium possesses special chemical stability.

Transition Metals The d-block elements are metals with typical metallic properties and are often referred to as transition elements.

Silver

The P-Block & Main Group Elements The p-block elements consist of all the elements of Groups 13–18 except helium. The p-block elements together with the s-block elements are called the main-group elements. At its right-hand end, the p block includes all of the nonmetals except hydrogen and helium. All six of the metalloids are also in the p block. At the left-hand side and bottom of the block, there are eight p-block metals. The properties of elements of the p block vary greatly.

Halogens The elements of Group 17 are known as the halogens. fluorine, chlorine, bromine, iodine, and astatine The halogens are the most reactive nonmetals. They react vigorously with most metals to form examples of the type of compound known as salts. The metalloids, or semiconducting elements, are located between nonmetals and metals in the p block. The metals of the p block are generally harder and denser than the s-block alkaline-earth metals, but softer and less dense than the d-block metals.

Chlorine

Lanthanides & Actinides In the periodic table, the f-block elements are wedged between Groups 3 and 4 in the sixth and seventh periods. Their position reflects the fact that they involve the filling of the 4f sublevel. The first row of the f block, the lanthanides, are shiny metals similar in reactivity to the Group 2 alkaline metals. The second row of the f block, the actinides, are between actinium and rutherfordium. The actinides are all radioactive.